This invention relates to a harvesting platform for an agricultural harvesting machine, such as a self-propelled combine and more particularly to a harvesting platform having a plurality of transversely spaced independently vertically adjustable areas on the platform, such as a flexible cutter bar or a platform with a plurality of independently vertically adjustable row units. U.S. Pat. No. 3,698,164 and U.S. Pat. application Ser. No. 523,509, also assigned to the assignee herein, are examples of flexible cutter bars, while U.S. Pat. No. 3,808,783, also assigned to the assignee herein, is an example of a platform with vertically adjustable row units. In the latter type machine, the row units are free to float independently of one another within a limited degree so that the row units follow the contour of the ground, while in the flexible cutter bars, the cutter bar is free to flex to a limited degree and the cutter bar is mounted on the platform by means of a number of transversely spaced mounting means that permit different areas of the cutter bar to adjust vertically relative to the adjacent areas, whereby the cutter bar follows the contour of the ground.
As is well known, the harvesting platforms are conventionally carried at the forward end of the vertically adjustable feeder house, the height of the feeder house and consequently of the platform being controlled by hydraulic cylinders operative between the feeder house and the main frame of the combine, the extension of the hydraulic cylinder normally being controlled by valving at the operator station. The flexible cutter bars and machines with vertically adjustable row units are designed so that the crop is harvested as close to the ground as possible, such platforms being particularly advantageous when used in harvesting soybeans or the like, and normally the operator positions the platform so that the row units or the flexible cutter bar rides along the ground, the flexibility or independent vertical adjustment allowing the harvesting elements to follow the contour of the ground. Normally the platform is positioned by the operator so that the harvesting elements are somewhere in the mid range of their vertical adjustment, so that the individual elements are free to move both upwardly and downwardly. Typically, the range of adjustment is approximately four inches, and during operation, it is normally necessary for the operator to frequently adjust the height of the platform to maintain the platform in its optimum position for vertical adjustment of the harvesting elements.
It is known to provide automatic control systems responsive to ground engaging feelers for controlling the hydraulic cylinders that establish the position of the platform to maintain the optimum position of the platform, and it is also known to provide an automatic height control system for a platform utilizing a flexible cutter bar, such as shown in U.S. Pat. No. 3,698,164. However, such automatic control systems are expensive and, depending on the sensitivity of the system, the automatic control systems produce frequent adjustments to the platform height, the constant hunting of the platform for the optimum height being unnecessary and irritating to the operator.